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Thread: XP-82 as a racer ?

  1. #21

    Default Re: XP-82 as a racer ?

    Tandem engines is the way to go for a twin engine configuration. No additional frontal area, just the extra weight, but twice the cube's and horsepower

  2. #22
    Join Date
    Jan 2004
    Location
    Texas, Oregon
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    639

    Default Re: XP-82 as a racer ?

    Quote Originally Posted by supercub View Post
    Tandem engines is the way to go for a twin engine configuration. No additional frontal area, just the extra weight, but twice the cube's and horsepower
    That was my thought, too, until I tried to find solid numbers for pusher prop efficiency at high speeds. In other words, it's not so simple as it would seem (your "twice the cube's and horsepower").

  3. #23
    Join Date
    Jul 2009
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    Key Biscayne
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    259

    Default Re: XP-82 as a racer ?

    Reno should add a turboprop class so the manufacturers trying to gain COIN contracts have an avenue to show off.

    It's not like their pockets aren't deep enough.

  4. #24

    Default Re: XP-82 as a racer ?

    The Do-335 propulsion configuration has been tested and proven to be a viable two engine lower drag concept. It just has to be a little smaller than the gigantic Do-335.
    John Slack

  5. #25

    Default Re: XP-82 as a racer ?

    I have some more information on my tandem push-pull concept here. There is an efficiency loss with the pusher, but you would have a lot of drag and rolling inertia loss with a conventional twin, so it still seems the tandem is better. There are still a number of issues to work through: a drive shaft to take the torque (or strong enough and draggy tail booms like the P-38) , tall enough landing gear to avoid a prop strike, provisions on the rear prop for emergency egress/bailing out.

    I agree that the push-pull configuration is the best twin engine configuration for a racer. And a new unlimited would have to be a twin if it were to use a non-1940s engine. No one makes aircraft piston engines big enough to compete because there is no demand for it anymore. (this issue would go away if turbo props were introduced. I think there is a lot of sponsorship/purse potential there and would encourage newer and most importantly safer designs)
    "young" Thomas

  6. #26

    Default Re: XP-82 as a racer ?

    When I mentioned tandem engines, I was thinking more along the lines of some of the early seaplane racers where they had 2 engine in tandem turning a tractor propeller. What about counter rotating props with one engine turning a different prop?

  7. #27
    Join Date
    May 2015
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    FINLAND
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    209

    Default Re: XP-82 as a racer ?

    Quote Originally Posted by CubersWrist View Post
    http://p38assn.org/Personnel/images/sketch.png
    http://p38assn.org/development.htm#

    Kelly Johnson considered the P-82 configuration when designing the P-38, so that gives you some idea of how it would do around the pylons. As a thought experiment I tried sketching a clean sheet racer that didn't depend on any warbird parts or engines (basically a second attempt at a Pond Racer style project). There is so much extra drag (frontal area and intersection area), system complexity, and weight, when you "add on" a second engine, it's almost not worth it.

    The electric motor in the spinner is bad, because now you're slinging around the motor inside the spinner. Something is going to break. Unless you have some power and weight numbers my initial thought is a hybrid system is more complexity, at more weight, for less power. And the electric motor would be very questionably legal.

    Yes it might be so...actually P-51H is the fastest piston plane in annals. In standard configuration.

    https://www.youtube.com/watch?v=LLufZc4j38M

    Above Pond Racer model.

  8. #28

    Default Re: XP-82 as a racer ?

    The MC72 had two V12s bolted together. Each engine turned its own prop and they were contra-rotating. Engine reliability wasn’t good but it lasted long enough to claim fastest seaplane.

    Hadn’t thought about tandem engines going to a single prop. I guess it’s been done before though so why not?
    "young" Thomas

  9. #29
    Join Date
    May 2015
    Location
    FINLAND
    Posts
    209

    Default Re: XP-82 as a racer ?

    Quote Originally Posted by CubersWrist View Post
    The MC72 had two V12s bolted together. Each engine turned its own prop and they were contra-rotating. Engine reliability wasn’t good but it lasted long enough to claim fastest seaplane.

    Hadn’t thought about tandem engines going to a single prop. I guess it’s been done before though so why not?
    Also a contra with just one engine was considered by Heinkel.

    Attachment 23970

    Topspeed of 880 km/h.

  10. #30

    Default Re: XP-82 as a racer ?

    That's completely different. You would need a big engine to have enough hp to merit turning an extra prop. But then if you have a big engine, then you also wouldn't need a twin engine configuration to begin with. You only go with contra-rotating on a single engine if you have more hp than your prop can use(limited by tip speed). And then you would have to analyze if the extra thrust from the second prop and gearbox would outweigh the drag from the extra weight.
    "young" Thomas

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